Sensing device having photo sensing element alternately operated in different biased states and related touch-controlled display device

ABSTRACT

The present invention provides a sensing device and a display device utilizing the sensing device. A photo sensing element of the sensing device is alternatively operated in a biased state and a reverse-biased state to prevent the stress issue. Furthermore, the sensing device improves the S/N ratio by generating an output signal through an active component. The display device including the sensing device prevents the stress issue and improves the S/N ratio by using specific driving signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims the benefit of U.S. patent application Ser. No. 13/103,999, filed May 9, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensing device, and more particularly, to a sensing device employed in a touch-controlled display device.

2. Description of the Prior Art

Touch-controlled display devices are widely used in various electronic products in the market. When the touch source touches the figures or objects on the touch screen, a sensing device of the touch-controlled display device judges an occurrence of a touch event, and then an internal processing system operates according to a program compiled in advance. Traditionally, sensing devices employed in touch-controlled display devices may be categorized into two different types as shown in FIG. 1 and FIG. 2.

Please refer to FIG. 1 first. The sensing device shown in the figure turns on the transistor M₂ mainly by the signal S₁ to charge the capacitor C. Then, a photo diode PD generates a leakage current having different intensity in response to different magnitude of the ambient light source, where the ambient light source has an instant magnitude change when there is a touch source approaching, and the leakage current would discharge the capacitor C to change a terminal voltage of the capacitor C. When the signal S₂ is raised to a high logic level, the terminal voltage of the capacitor C is raised, and the output voltage V_(out) is changed correspondingly. Therefore, checking the voltage level of the output voltage V_(out) can judge whether a touch event occurs. However, regarding this type of sensing device, since the photo diode PD stays in a biased state for a long period of time, the electric charges are accumulated in a PN junction of the photo diode PD or the occurrence probability of defect states is increased, leading to a shifted I-V curve of the photo diode PD. Consequently, it is hard to control the relationship between the discharging extent of the capacitor C and the magnitude of the ambient light source, which affects the accuracy of the touch event judgment.

Moreover, the sensing device shown in FIG. 2 also judges whether a touch event occurs by charging the capacitor C and then discharging the capacitor C. However, this type of sensing device discharges the capacitor C by a photo-transistor M₂, and the discharging extent is also affected by the magnitude of the ambient light source. The photo-transistor M₂ is biased mainly by fixed voltages V_(B1) and V_(B2), and thus continuously operates in the biased state. Besides, the output voltage V_(out) is generated directly according to the terminal voltage of the capacitor C through the transistor M₁, and then the touch event is judged according to the output voltage V_(out). Regarding this type of sensing device, the photo-transistor M₂ also stays in the biased state for a long period of time. Therefore, the electric charges are accumulated in a junction of the photo-transistor M₂ or the occurrence probability of defect states is increased, leading to a shifted I-V curve of the photo-transistor M₂. Consequently, it is hard to control the relationship between the discharging extent of the capacitor C and the magnitude of the ambient light source, which affects the accuracy of the touch event judgment. Moreover, the output signal V_(out) is generated directly according to the terminal voltage of the capacitor C. In the generating process of the output signal V_(out), the terminal voltage of the capacitor C may have a slight variation because of the continuous generation of the leakage current. This also affects the accuracy of the touch event judgment. It can be readily known from the two examples mentioned above that the conventional design still has room for improvement.

SUMMARY OF THE INVENTION

In view of above, the present invention provides an innovative sensing device that may avoid the disadvantage of the conventional sensing device design. The characteristic of the present invention is that by a proper design of a biased signal which changes the biased state of the photo sensing element, alternately, the electric charges accumulated in the photo sensing element are released to thereby prevent the stress issue and accordingly solve the shifted I-V curve issue. Moreover, the present invention generates output signals by active components to thereby increase the overall signal-to-noise (S/N) ratio, and properly uses the control signal of the display device disposed in the sensing device as a biased signal to thereby save the cost of implementing an additional control circuit and improve the aperture ratio.

Since the photo sensing element may be an element having a two-terminal structure (e.g., a diode) or an element having a three-terminal structure (e.g. a transistor), different embodiments of the present invention therefore provide driving control signals of different timings to change the biased states of the photo sensing element that has a two-terminal structure or three-terminal structure, in order to solve the issue encountered by the conventional sensing device design.

According to one exemplary embodiment, a sensing device comprises: a photo sensing element, having a first terminal for receiving a second signal and a control terminal for receiving a first signal, and a second terminal; a first capacitor, having a first electrode electrically connected to the second terminal of the photo sensing element and a second electrode electrically connected to a third signal; and a first transistor, electrically connected to the second terminal of the photo sensing element and having a first terminal, a control terminal and a second terminal. Additionally, the first signal and the second signal are both driving signals each supporting two logic levels, and a voltage value corresponding to a high logic level of the first signal is higher than a voltage value corresponding to a high logic level of the second signal; and a voltage value corresponding to a low logic level of the first signal is not higher than a voltage value corresponding to a low logic level of the second signal.

According to another exemplary embodiment, a sensing device comprises: a photo sensing element, having a first terminal and a control terminal for receiving a first signal, wherein the first terminal of the photo sensing element is electrically connected to a second signal through at least one other element. The first signal and the second signal are both driving signals each supporting two logic levels, and a logic level transition of the first signal is not synchronized with a logic level transition of the second signal.

According to still another exemplary embodiment, a sensing device comprises: a photo sensing element, having a first terminal and a control terminal for receiving a first signal, wherein the first signal is a driving signal that supports two logic levels; and a first capacitor, having a first electrode electrically connected to the first terminal of the photo sensing element and a second electrode; and a first transistor electrically connected to the first terminal of the photo sensing element and having a first terminal, a control terminal and a second terminal.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a conventional sensing device.

FIG. 2 is a circuit diagram of another conventional sensing device.

FIG. 3 is a diagram illustrating a circuit structure of a first exemplary embodiment of a sensing device according to the present invention and transition timing of control signals of the sensing device.

FIG. 4 is a diagram illustrating a circuit structure of a second exemplary embodiment of the sensing device according to the present invention and transition timing of control signals of the sensing device.

FIG. 5 is a circuit diagram of a third exemplary embodiment of the sensing device according to the present invention.

FIG. 6 is a circuit diagram of a fourth exemplary embodiment of the sensing device according to the present invention.

FIG. 7 is a diagram illustrating a circuit structure of a fifth exemplary embodiment of the sensing device according to the present invention and transition timing of control signals of the sensing device.

FIG. 8 is a diagram illustrating one exemplary embodiment of a display device according to the present invention.

FIG. 9 is a diagram illustrating another exemplary embodiment of the display device according to the present invention.

FIG. 10 is a waveform diagram of control signals according to another exemplary embodiment of the present invention.

FIG. 11 is a waveform diagram of control signals according to yet another exemplary embodiment of the present invention.

FIG. 12 is a circuit diagram of a sixth exemplary embodiment of the sensing device according to the present invention.

FIG. 13 is a circuit diagram of a seventh exemplary embodiment of the sensing device according to the present invention.

FIG. 14 is a circuit diagram of an eighth exemplary embodiment of the sensing device according to the present invention.

FIG. 15 is a circuit diagram of a ninth exemplary embodiment of the sensing device according to the present invention.

DETAILED DESCRIPTION

The concept of the present invention is illustrated with reference to different exemplary embodiments and relevant figures. Elements or devices with the same reference numeral in different figures have similar operation principles and technical effects. Thus, repeated description is omitted below for brevity. Moreover, different technical features mentioned in different exemplary embodiments are not limited to the exemplary embodiments only. In fact, in a reasonable scope of the present invention, one of the exemplary embodiments may be properly modified to have specific technical features of other exemplary embodiments.

FIG. 3 shows the first exemplary embodiment of the sensing device according to the present invention. The sensing device includes a photo sensing element that has a three-terminal structure. The photo sensing element may be a photo-transistor; therefore, in the illustration below, the transistor TFT₁ is used to represent the photo sensing element that has a three-terminal structure. However, it is not the only limitation to the photo sensing element that has a three-terminal structure of the present invention. In other exemplary embodiments of the present invention, the photo sensing element may be realized by any three-terminal photo sensing element except for the transistor. The sensing device 100 includes a first transistor TFT₁, a second transistor TFT₂ and a first capacitor C₁. The first transistor TFT₁ has a first terminal E₁₁, a control terminal G₁ and a second terminal E₁₂. The second transistor TFT₂ has a first terminal E₂₁, a control terminal G₂ and a second terminal E₂₂. The first capacitor C₁ has a first electrode CE₁₁ and a second electrode CE₁₂. The control terminal G₁ of the first transistor TFT₁ is utilized for receiving a first signal S₁, and the second terminal E₁₂ of the first transistor TFT₁ is utilized for receiving a second signal S₂. The control terminal G₂ of the second transistor TFT₂ is electrically connected to the first terminal E₁₁ of the first transistor TFT₁. The second transistor TFT₂ is electrically connected to read circuit (not shown in the figure), and the read circuit judges whether a touch event happens on the sensing device 100 according to the output current I_(DS) that is generated when the second transistor TFT₂ is conductive. The first electrode CE₁₁ of the first capacitor C₁ is electrically connected to the first terminal E₁₁ of the first transistor TFT₁ and the control terminal G₂ of the second transistor TFT₂. Besides, the second electrode CE₁₂ of the first capacitor C₁ is electrically connected to a third signal S₃. The first signal S₁ and the second signal S₂ are driving signals each supporting two logic levels, and the first signal S₁ and the second signal S₂ are signals that have different voltage values, and may change the biased state of the first transistor TFT₁ (i.e., the photo sensing element), alternately. Besides, the logic level transition timing of the third signal S₃ is different from the logic level transition timing of each of the first signal S₁ and the second signal S₂.

Please refer to the lower part of FIG. 3 for exemplary illustration of the logic level transition timing of signals S₁-S₃. As can be known from the figure, when the sensing device 100 is operated at the resetting phase (T₁), the first signal S₁ is raised to a high logic level H₁, and the second signal S₂ is also raised to a high logic level H₂, which makes the first transistor TFT₁ stay in a forward-biased state. Meanwhile, the first capacitor C₁ is charged through the first transistor TFT₁, thereby raising the terminal voltage V_(a). When charging of the capacitor C₁ is finished, the sensing device 100 is operated at the sensing phase (T₂) ; meanwhile, the first signal S₁ is lowered to a low logic level L₁, and the second signal S₂ is also lowered to a low logic level L₂, which makes the first transistor TFT₁ stay in a reverse-biased state. Meanwhile, the voltage value corresponding to the low logic level L₁ is not higher than the voltage value corresponding to the low logic level L₂. Thus, the first transistor TFT₁ generates a leakage current to discharge the first capacitor C₁, and the terminal voltage V_(a) is reduced accordingly. Since the first transistor TFT₁ is a photo sensing element, the intensity of the leakage current changes with the ambient light source. When a touch event happens on the sensing device 100, the ambient light source is shaded, and the leakage current of the first transistor TFT₁ is decreased accordingly; otherwise, the leakage current of the first transistor TFT₁ is comparatively large. After a period of time, the sensing device 100 enters a read phase (T₃) . In this operational phase, the first signal S₁ and the second signal S₂ still maintain at the low logic levels L₁ and L₂, respectively, and the third signal S₃ is raised to a high logic level H₃. This voltage is coupled to the first capacitor C₁, and therefore raises the terminal voltage V_(a) to make the second transistor TFT₂ conductive. An output current I_(DS) is generated accordingly. The intensity of the output current I_(DS) is relevant to the terminal voltage V_(a), it is charged to the highest level at the resetting phase and then reduced due to discharging at the following sensing phase and read phase, and a voltage level corresponding to the high logic level H₃ of the third signal S₃. Finally, the read circuit judges whether a touch event happens on the sensing device 100 according to the intensity of the output current I_(DS).

The first signal S₁ is synchronized with the second signal S₂ in this exemplary embodiment; however, in other exemplary embodiments of the present invention, the first signal S₁ may not be synchronized with the second signal S₂. When the first signal S₁ is not synchronized with the second signal S₂, the pulse falling edge timing corresponding to the second signal S₂ may be equal to the pulse falling edge timing corresponding to the first signal S₁. One of the possible relations is shown in FIG. 10, wherein the timing at which the second signal S₂ has a transition from the low logic level L₂ to the high logic level H₁ lags behind the timing at which the first signal S₁ has a transition from the low logic level L₁ to the high logic level H₁; moreover, the timing at which the second signal S₂ has a transition from the high logic level H₂ to the low logic level L₂ may be equal to or lag behind the timing at which the first signal S₁ has a transition from the high logic level H₁ to the low logic level L₁. In the exemplary embodiment shown in FIG. 10, the third signal S3 is the one shown in FIG. 3, and is raised to a high logic level H₃ when the sensing device 100 enters the read phase (T₃). Further description is omitted here for brevity.

Moreover, the pulse falling edge timing corresponding to the second signal S₂ may also lag behind the pulse falling edge timing corresponding to the first signal S₁, and one of the possible relations is shown in FIG. 11. In this exemplary embodiment, the pulse falling edge timing corresponding to the second signal S₂ lags behind the pulse falling edge timing corresponding to the first signal S₁. Please note that the timing at which the second signal S₂ has a transition from the low logic level L₂ to the high logic level H₂ is not within the time period during which the third signal S₃ has the high logic level H₃. However, it is only one possible embodiment of the present invention, and is not meant to be the only variation of the present invention.

The relationship of voltage values corresponding to logic levels of the signals S₁-S₃ is detailed as follows. In order to alternately change the biased state of the first transistor TFT₁, i.e., to make the first transistor TFT₁ alternately operated at the forward-biased state and the reverse-biased state, the voltage value corresponding to the high logic level H₁ of the first signal S₁ must be higher than the voltage value corresponding to the high logic level H₂ of the second signal S₂, which is for making the first transistor TFT₁ operated at the forward-biased state. The voltage value corresponding to the low logic level L₁ of the first signal S₁ must not be higher than the voltage value corresponding to the low logic level L₂ of the first signal S₂, which is for making the first transistor TFT₁ operated at the reverse-biased state. Besides, as the sensing device 100 is still operated at the resetting phase when the second signal S₂ has the high logic level H₂, the second transistor TFT₂ is not allowed to be conductive at this moment, in order to prevent a false judgment of the touch event. However, when the second signal S₂ has the high logic level H₂, the terminal voltage V_(a) is inevitably raised. Hence, the selection of the voltage value corresponding to the high logic level H₂ of the second signal S₂ must ensure that the second transistor TFT₂ would not be conductive.

Besides, the sensing device of the present exemplary embodiment is disposed in a touch-controlled display device to act as a necessary touch sensing means in practice. Please refer to FIG. 8. The touch-controlled display device 800 includes a plurality of pixel elements 815 arranged in a matrix, a read circuit 830 and a plurality of sensing devices 100 arranged in a matrix. Besides, the touch-controlled display device 800 further includes a plurality of scan lines GL₁-GL_(N), a plurality of data lines DL₁-DL_(N), and a plurality of read lines RL₁-RL_(N) electrically connected to the read circuit 830. The pixel elements 815 are mainly utilized for displaying images to be displayed. The scan lines GL₁-GL_(N) and the data lines DL₁-DL_(N) are utilized for receiving scan line driving signals generated from gate drivers and data line signals generated from source drivers, respectively, and are utilized for controlling the pixel elements 815 to perform the image display operation. Since those skilled in the art should readily understand operations and principles of these circuit elements, further description is omitted here for brevity.

The arrangement of sensing devices 100 is similar to that of pixel elements 815. In the present invention, driving signals on the scan lines GL₁-GL_(N) are utilized for acting as the first signal S₁ to bias the sensing devices 100. Thus, sensing devices 100 are respectively connected to the scan lines GL₁-GL_(N), as shown in FIG. 8. The control terminals G₁ of the first transistors TFT₁ in the sensing devices 100 receive driving signals on scan lines GL₁-GL_(N). Moreover, the first transistor TFT₁ in each of the sensing devices 100 is forward-biased and reverse-biased alternately according to one of the driving signals on the scan lines GL₁-GL_(N), while the read circuit 830 reads sensing results (e.g., the output current I_(DS)) generated by the sensing devices 100 through the read lines RL₁-RL_(N). Therefore, in this exemplary embodiment, the signal generating circuit or driving circuit required for generating the first signals S₁ may be omitted. In this exemplary embodiment, the third signal S₃ is preferably independent of driving signals on the scan lines GL₁-GL_(N). More specifically, in a case where the voltage value corresponding to the high logic level H₃ of the third signal S₃ is too high, once it is coupled to the first capacitor C₁, the terminal voltage V_(a) generated at the sensing phase is raised excessively, which makes the second transistor TFT₂ fail to generate the output current I_(DS) with proper intensity corresponding to the present ambient light source at the read phase.

It should be noted that in the first exemplary embodiment of the present invention, the terminal voltage V_(a) is electrically connected to the control terminal of the second transistor TFT₂; however, this is not meant to be a limitation of the present invention. In other exemplary embodiments, the terminal voltage V_(a) may be electrically connected to the first terminal E₂₁ or the second terminal E₂₂ of the second transistor TFT₂. Both alternative designs fall into the scope of the present invention.

The second exemplary embodiment of the present invention provides a sensing device as shown in FIG. 4. In this exemplary embodiment, an extra element is added to the circuit structure of the sensing device 100 in the first exemplary embodiment, and the third signals S₃ is realized by using the driving signals on the scan lines GL₁-GL_(N) and thereby save the signal generating circuit or driving circuit required for generating the third signals S₃. The possible exemplary implementation is detailed below. The sensing device 200 includes a first transistor TFT₁, a second transistor TFT₂, a first capacitor C₁ and a second capacitor C₂. The first transistor TFT₁ has a first terminal E₁₁, a control terminal G₁ and a second terminal E₁₂. The second transistor TFT₂ has a first terminal E₂₁, a control terminal G₂ and a second terminal E₂₂. The first capacitor C₁ has a first electrode CE₁₁ and a second electrode CE₁₂, and the second capacitor C₂ has a first electrode CE₂₁ and a second electrode CE₂₂. The first transistor TFT₁ is a photo-transistor. The control terminal G₁ of the first transistor TFT₁ is utilized for receiving a first signal S₁, and the second terminal E₁₂ of the first transistor TFT₁ is utilized for receiving a second signal S₂. The control terminal G₂ of the second transistor TFT₂ is electrically connected to the first terminal E₁₁ of the first transistor TFT₁. The second transistor TFT₂ is electrically connected to a read circuit (not shown in the figure), and the read circuit judges whether a touch event happens on the sensing device 200 according to the output current I_(DS) that is generated when the second transistor TFT₂ is conductive. The first electrode CE₁₁ of the first capacitor C₁ and the first electrode CE₂₁ of the second capacitor C₂ are electrically connected to the first terminal E₁₁ of the first transistor TFT₁ and the control terminal G₂ of the second transistor TFT₂. The second electrode CE₁₂ of the first capacitor C₁ is electrically connected to the third signal S₃, and the second electrode CE₂₂ of the second capacitor C₂ is electrically connected to the fourth signal S₄. The first signal S₁ and the second signal S₂ are driving signals each supporting two logic levels, and are used to change the biased state of the first transistor TFT₁, alternately. The logic level transition timing of the third signal S₃ is different from the logic level transition timing of the first signal S₁ and second signal S₂, and the fourth signal S₄ is a direct current (DC) level signal.

Please refer to the lower part of FIG. 4 for illustration of the logic level transition timing of signals S₁-S₃. As can be known from the figure, when the sensing device 200 is operated at the resetting phase (T₁), the first signal S₁ is raised to a high logic level H₁, and the second signal S₂ is also raised to a high logic level H₂, which makes the first transistor TFT₁ stay in a forward-biased state. Meanwhile, the first capacitor C₁ and the second capacitor C₂ are both charged through the first transistor TFT₁, and the terminal voltage V_(a) is raised accordingly. When the charging of the first capacitor C₁ and the second capacitor C₂ is finished, the sensing device 200 is operated at the sensing phase (T₂); meanwhile, the first signal S₁ is lowered to a low logic level L₁, and the second signal S₂ is also lowered to a low logic level L₂, which makes the first transistor TFT₁ stay in a reverse-biased state. Thus, the first transistor TFT₁ generates a leakage current to discharge the first capacitor C₁ and the second capacitor C₂, thereby reducing the terminal voltage V_(a). Since the first transistor TFT₁ is a photo-transistor, the intensity of the leakage current changes with the ambient light source. When a touch event happens on the sensing device 200, the ambient light source is shaded, and the leakage current of the first transistor TFT₁ is reduced; otherwise, the leakage current of the first transistor TFT₁ is increased. After a period of time, the sensing device 200 enters a read phase (T₃). In this operational phase, the first signal S₁ and the second signal S₂ still maintain at the low logic levels L₁ and L₂, respectively, and the third signal S₃ is raised to a high logic level H₃. This voltage is coupled to the first capacitor C₁ and the second capacitor C₂, and therefore raises the terminal voltage V_(a) to make the second transistor TFT₂ conductive. Consequently, an output current I_(DS) is generated, where the intensity of the output current I_(DS) is relevant to the terminal voltage V_(a), which is charged to the highest level at the resetting phase and then reduced due to discharging at the following sensing phase and read phase, and a voltage value corresponding to the high logic level H₃ of the third signal S₃. Finally, the read circuit judges whether a touch event happens on the sensing device 200 according to the intensity of the output current I_(DS).

In this exemplary embodiment, the first signal S₁ is synchronized with the second signal S₂; however, in other exemplary embodiments of the present invention, the first signal S₁ may not be synchronized with the second signal S₂. When the first signal S₁ is not synchronized with the second signal S₂, the pulse falling edge timing corresponding to the second signal S₂ may be equal to the pulse falling edge timing corresponding to the first signal S₁ as shown in FIG. 10, but the pulse falling edge timing corresponding to the second signal S₂ is required to be maintained above a certain level, in order to ensure that the voltage level of the second signal S₂ is fully charged while the first signal S₁ has the high logic level H₁.

In the second exemplary embodiment of the present invention, the operation thereof is almost similar to that of the first exemplary embodiment. Since the second capacitor C₂ and the fourth signal S₄ are specially added in the second exemplary embodiment, the third signals S₃ may be realized by the driving signals on the scan lines GL₁-GL_(N) in order to save the signal generating circuit or driving circuit required for generating the third signals S₃.

Of course, the logic level transition timing of signals in the second exemplary embodiment of the present invention may also be similar to that shown in FIG. 10 or FIG. 11. The relationship of voltage values corresponding to logic levels of the signals is detailed as follows. In order to alternately change the biased state of the first transistor TFT₁ (e.g., to make the first transistor TFT₁ alternately operated at the forward-biased state and the reverse-biased state), the voltage value corresponding to the high logic level H₁ of the first signal S₁ must be higher than the voltage value corresponding to the high logic level H₂ of the first signal S₂ (to make the first transistor TFT₁ operated at the forward-biased state), and the voltage value corresponding to the low logic level L₁ of the first signal S₁ must not be higher than the voltage value corresponding to the low logic level L₂ of the first signal S₂ (to make the first transistor TFT₁ operated at the reverse-biased state). Besides, when the second signal S₂ has the high logic level H₂, the sensing device 200 is still operated at the resetting phase. Therefore, the second transistor TFT₂ is not allowed to be conductive, in order to prevent a false judgment of the touch event. However, when the second signal S₂ has the high logic level H₂, the terminal voltage V_(a) is inevitably raised. Thus, the selection of the voltage value corresponding to the high logic level H₂ of the second signal S₂ should ensure that the second transistor TFT₂ would not be conductive. Moreover, the selection of the voltage value of the fourth signal S₄ is not limited in the present exemplary embodiment as long as the voltage value is a DC level.

Similarly, in the second exemplary embodiment of the present invention, the terminal voltage V_(a) is electrically connected to the control terminal of the second transistor TFT₂; however, this is not meant to be a limitation of the present invention. In another exemplary embodiment, the terminal voltage V_(a) may be electrically connected to the first terminal E₂₁ or the second terminal E₂₂ of the second transistor TFT₂. Both alternative designs fall within the scope of the present invention.

More specifically, the difference between the first exemplary embodiment and the second exemplary embodiment of the present invention is that the first signal S₁ and the third signal S₃ in the second exemplary embodiment both may be replaced by driving signals on the scan lines. The first capacitor C₁ and the second capacitor C₂ form a voltage divider. Therefore, when the high logic level H₃ of the third signal S₃ is coupled to the first capacitor C₁ and the second capacitor C₂, the terminal voltage V_(a) generated at the sensing phase will not be over raised, and the intensity of the output current I_(DS) corresponding to the present ambient light source and passing through the second transistor TFT₂ in the read phase. Moreover, if the first signal S₁ and the third signal S₃ are both replaced by the scan line driving signals, the relation between the voltage levels of the signals S₁-S₃ is detailed as below. As the first signal S₁ and the third signal S₃ are driving signals having the same voltage level, the voltage value corresponding to the high logic level H₁ of the first signal S₁ is equal to the voltage value corresponding to the high logic level H₃ of the third signal S₃, and the voltage value corresponding to the low logic level L₁ of the first signal S₁ is equal to the voltage value corresponding to the low logic level L₃ of the third signal S₃. Moreover, the voltage values corresponding to the low logic level L₁ of the first signal S₁ and the low logic level L₃ of the third signal S₃ are not higher than the voltage value corresponding to the low logic level L₂ of the second signal S₂, and the voltage values corresponding to the high logic level H₁ of the first signal S₁ and the high logic level H₃ of the third signal S₃ are higher than the voltage value corresponding to the high logic level H₂ of the second signal S₂.

The exemplary implementation of disposing the sensing device of the present invention in a touch-controlled display device is illustrated below. Please refer to FIG. 9. The touch-controlled display device 900 includes a plurality of pixel elements 915 arranged in a matrix, a read circuit 930 and a plurality of sensing devices 200 arranged in a matrix. Besides, the touch-controlled display device 900 further includes a plurality of scan lines GL₁-GL_(N), a plurality of data lines DL₁-DL_(N), and a plurality of read lines RL₁-RL_(N) coupled to the read circuit 930. The pixel elements 915 are mainly utilized for displaying images to be displayed. The driving signals of the scan lines GL₁-GL_(N) and the data lines DL₁-DL_(N) are respectively generated by gate drivers and source drivers, and are utilized for controlling the pixel elements 915 to perform image display operation. Since those skilled in the art should readily understand the operations and principals of these circuit elements, further description is omitted here for brevity.

The arrangement of sensing devices 200 is similar to that of pixel elements 915. In present invention, driving signals on the scan lines GL₁-GL_(N) are utilized for acting as the first signal S₁ and the third signal S₃ to bias the sensing devices 200. Thus, sensing devices 200 are respectively connected to the scan lines GL₁-GL_(N), as shown in FIG. 9. The control terminals G₁ of the first transistors TFT₁ in the sensing devices 200 and the second electrodes CE₁₂ of the first capacitors C₁ in the sensing devices 200 receive driving signals on scan lines GL₁-GL_(N). Moreover, the first transistor TFT₁ in each of the sensing devices 200 is forward-biased and reverse-biased alternately according to the driving signals on the scan lines GL₁-GL_(N), while the read circuit 930 reads sensing results (e.g., the output current I_(DS)) generated by the sensing devices 200 through the read lines RL₁-RL_(N). Therefore, in this exemplary embodiment, the signal generating circuit or driving circuit required for generating the first signals S₁ and the third signals S₃ may be omitted. Besides, as can be known from the transition timing shown in FIG. 4, the first signal S₁ lags behind the third signal S₃. Therefore, the third signal S₃ is a driving signal on a scan line that has a higher priority among the scan lines (In other words, the first signal S₁ and the third signal S₃ are different scan line driving signals). For example, if the third signal S₃ is replaced with a driving signal of the scan line GL₁, the first signal S₁ is replaced with a driving signal of the scan line GL_(i+1).

Besides, in order to increase the S/N ratio of the sensing device, the third exemplary embodiment and the fourth exemplary embodiment, respectively shown in FIG. 5 and FIG. 6, are provided in the present invention according to the first exemplary embodiment and the second exemplary embodiment. Compared with the first exemplary embodiment and the second exemplary embodiment, the sensing devices 300 and 400 in the third exemplary embodiment and the fourth exemplary embodiment of the present invention have the third transistors TFT3 disposed at the output terminals of the second transistors TFT₂ (e.g., the second terminals E₂₂), which may prevent interference situations as below. Please refer to FIG. 8 or FIG. 9. When the read circuit 830 or 930 reads the output current I_(DS) from the sensing device 100 or 200 in the matrix of sensing devices through the read line RL_(i), the original read operation will be disturbed if other sensing device 100 or 200 also outputs a current to the same read line RL_(i). Therefore, the third transistor TFT₃ is capable of isolating an output of the second transistor TFT₂ in each sensing device 300 or 400. Only when the sensing device 300 or 400 is operated at the read phase, the third transistor TFT₃ is turned on by the control signal Ctrl, thereby allowing the output current I_(DS) to be output to the read line RL_(i). In this way, the cross-interference is avoided, and the S/N ratio is improved. Besides, since the third exemplary embodiment and the fourth exemplary embodiment of the present invention may also be controlled by the scan lines of pixels that are employed in the first exemplary embodiment and the second exemplary embodiment, further description is omitted here for brevity.

The fifth exemplary embodiment of the present invention provides a sensing device that does not use any active component to generate the output signal, such as the sensing device 500 shown in FIG. 7. The sensing device 500 does not include the second transistor TFT₂ in the aforementioned exemplary embodiments. In this exemplary embodiment, the terminal voltage V_(a) corresponding to the first capacitor C₁ is directly utilized as the output signal, the output signal is coupled to the read line RL_(i) through the third transistor TFT₃, and the coupling timing of the terminal voltage (i.e., the conductive state of the third transistor TFT₃) is controlled through the signal Ctrl to maintain a certain S/N ratio. The first transistor TFT₁ may be biased by the first signal S₁ and the second signal S₂ to stay in the forward-biased state and the reverse-biased state alternately. Moreover, the sensing device 500 may also be disposed in the touch-controlled display device as mentioned above.

In the exemplary embodiments mentioned above, the sensing devices of the present invention are all implemented by photo sensing elements each having a three-terminal structure. However, by using different configuration of the control signal, a photo sensing element having a two-terminal structure maybe utilized, and the biased state of the photo sensing element having a two-terminal structure may be changed alternately, wherein the photo sensing element having a two-terminal structure may be a photo-diode or a silicon rich oxide (SRO) element. Please refer to the illustration as follows. As the photo sensing element that has a two-terminal structure includes only two terminals to control its biased state, the sixth exemplary embodiment and the seventh exemplary embodiment of the present invention therefore provide a technical means which allows the two-terminal photo sensing element in the sensing device to stay in the forward-biased state and reverse-biased state alternately by using the first signal S1 only. Please refer to the sensing devices 600 and 700 shown in FIG. 12 and FIG. 13. FIG. 12 shows the sixth exemplary embodiment of the present invention. In this exemplary embodiment, the sensing device 600 includes a first transistor TFT₁, a first capacitor C₁ and a second transistor TFT₂. The control terminal G₁ of the first transistor TFT₁ is coupled to the second terminal E₁₂ of the first transistor TFT₁ to form a two-terminal photo sensing element. Meanwhile, the control terminal G₁ and the second terminal E₁₂ of the first transistor TFT₁ both receive the first signal S₁. Hence, when the first signal S₁ has a high logic level H₁, the first transistor TFT₁ stays in the forward-biased state, and when the first signal S₁ has a low logic level L₁, the first transistor TFT₁ stays in the reverse-biased state. FIG. 13 shows the seventh exemplary embodiment of the present invention. In this exemplary embodiment, the sensing device further includes a second capacitor C₂ electrically connected to the first terminal E₁₁ of the first transistor TFT₁. The sixth exemplary embodiment and the seventh exemplary embodiment of the present invention may reach the same technical effect of the aforementioned exemplary embodiments by changing the terminal signal of the transistor TFT₁. As the voltage level of the third signal S₃ in the sixth exemplary embodiment and the seventh exemplary embodiment is similar to that of the aforementioned exemplary embodiments, further description is omitted here for brevity.

Similarly, in the sixth exemplary embodiment and the seventh exemplary embodiment of the present invention, the terminal voltage V_(a) is electrically connected to the control terminal G₂ of the second transistor TFT₂. However, in other exemplary embodiments of the present invention, the terminal voltage V_(a) may be electrically connected to the first terminal E₂₁ or the second terminal E₂₂ of the second transistor TFT₂.

Moreover, according to the signal configuration mentioned above, the photo sensing element of the sensing device according to the present invention may be a photo diode or other photo semiconductor element. Please refer to FIG. 14 and FIG. 15. FIG. 14 shows the eighth exemplary embodiment of the present invention. In this exemplary embodiment, a first terminal E₁₁ of the photo semiconductor element PSD of the sensing device 800 is electrically connected to the control terminal G₂ of the second transistor TFT₂ and the first electrode CE₁₁ of the first capacitor C₁, and a second terminal E₁₂ of the photo semiconductor element PSD is utilized for receiving the first signal S₁. FIG. 15 shows the ninth exemplary embodiment of the present invention. In this exemplary embodiment, a first terminal E₁₁ of the photo semiconductor element PSD of the sensing device 900 is coupled to the control terminal G₂ of the second transistor TFT₂, the first electrode CE₁₁ of the first capacitor C₁ and the first electrode CE₂₁ of the second capacitor C₂, and a second terminal E₁₂ of the photo semiconductor element PSD is utilized for receiving the first signal S₁.

When the first signal S₁ has a high logic level H₁, the photo semiconductor element PSD stays in a forward-biased state, and when the first signal S₁ has a low logic level L₁, the photo semiconductor element PSD stays in a reverse-biased state. It should be noted that the implementation of the photo semiconductor element PSD is not limited in the present invention. Any semiconductor element with photo sensing effect may be utilized in the exemplary embodiment of the present invention.

Similarly, in the eighth exemplary and the ninth exemplary of the present invention, the terminal voltage V_(a) is electrically connected to the control terminal G₂ of the second transistor TFT₂. However, in other exemplary embodiments of the present invention, the terminal voltage V_(a) may be electrically connected to the first terminal E₂₁ or the second terminal E₂₂ of the second transistor TFT₂.

Please note that the different technical features mentioned in the aforementioned exemplary embodiments are not limited to these exemplary embodiments only. In fact, within the reasonable scope of the present invention, proper modification may be made to one exemplary embodiment to make the exemplary embodiment have specific technical features of other exemplary embodiments. For example, regarding the sixth exemplary embodiment to the ninth exemplary embodiment, an extra third transistor TFT₃ may be added at the output terminal of the second transistor TFT₂ (i.e., the first terminal E₂₁ or the second terminal E₂₂) to isolate the output current I_(DS) of each sensing device, thereby improving the S/N ratio. Besides, similar to the first exemplary embodiment to the fifth exemplary embodiment, the sixth exemplary embodiment to the ninth exemplary embodiment of the present invention may also be disposed in a display device.

To sum up, the alternating current (AC) signal characteristic of the first signal S₁ or/and the second signal S₂ in the present invention is utilized for making the transistor in the sensing device stay in the forward-biased state and the reverse-biased state alternately, in order to prevent the stress issue. Besides, the driving signals on scan lines of the display device may be utilized for controlling transistors in the sensing devices to thereby save the cost of a signal generating circuit. Moreover, an output signal may be generated through an active component to thereby improve the S/N ratio of the sensing device.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A sensing device, comprising: a photo sensing element, having a first terminal and a control terminal, wherein the control terminal is configured to receive a first signal, and the first terminal of the photo sensing element is electrically connected to a second signal through at least one other element; wherein the first signal and the second signal are both driving signals each supporting two logic levels, and a logic level transition of the first signal is not synchronized with a logic level transition of the second signal.
 2. The sensing device of claim 1, wherein the photo sensing element is a photo diode or a silicon rich oxide (SRO) element.
 3. The sensing device of claim 1, wherein the at least one other element is a first capacitor having a first electrode electrically connected to the first terminal of the photo sensing element and a second electrode electrically connected to the second signal, and the first terminal of the photo sensing element receives the second signal through the first capacitor; and the sensing device further comprises a first transistor electrically connected to the first terminal of the photo sensing element and having a first terminal, a control terminal and a second terminal.
 4. The sensing device of claim 3, wherein when the first signal has a high logic level, the first transistor is not conductive.
 5. The sensing device of claim 3, wherein the first transistor is electrically connected to the first terminal of the photo sensing element through the control terminal of the first transistor, and the control terminal of the first transistor is electrically connected to the first electrode of the first capacitor.
 6. The sensing device of claim 3, further comprising: a second capacitor, having a first electrode electrically connected to the first electrode of the first capacitor and a second electrode.
 7. The sensing device of claim 3, further comprising: a second transistor, having a first terminal electrically connected to a second terminal of the first transistor, a control terminal for receiving a control signal and a second terminal electrically connected to a data read line, wherein the control signal is utilized for controlling a conductive state of the second transistor.
 8. A touch-controlled display device, comprising: a plurality of scan lines for receiving scan line driving signals; a plurality of data lines; a plurality of sensing devices of claim 3 arranged in a matrix, each of the plurality of sensing devices being coupled to at least one of the plurality of scan lines; and a plurality of pixel elements arranged in a matrix, each of the plurality of pixel elements being coupled to one of the plurality of scan lines and to one of the plurality of data lines, respectively.
 9. The touch-controlled display device of claim 8, wherein each of the sensing devices further comprises: a second capacitor, having a first electrode electrically connected to the first electrode of the first capacitor and a second electrode; wherein the first signal and the second signal are different scan line driving signals of the scan line driving signals, and an activation timing of the second signal is prior to an activation timing of the first signal.
 10. A sensing device, comprising: a photo sensing element, having a first terminal and a control terminal for receiving a first signal, wherein the first signal is a driving signal that supports two logic levels; a first capacitor, having a first electrode electrically connected to the first terminal of the photo sensing element and a second electrode; and a first transistor electrically connected to the first terminal of the photo sensing element and having a first terminal, a control terminal and a second terminal.
 11. The sensing device of claim 10, wherein the first transistor is electrically connected to the first terminal of the photo sensing element through the first terminal of the first transistor, and the first terminal of the first transistor is electrically connected to the first electrode of the first capacitor.
 12. A touch-controlled display device, comprising: a plurality of scan lines for receiving scan line driving signals; a plurality of data lines; a plurality of sensing devices of claim 10 arranged in a matrix, each of the plurality of sensing devices being coupled to at least one of the plurality of scan lines; and a plurality of pixel elements arranged in a matrix, each of the plurality of pixel elements being coupled to one of the plurality of scan lines and to one of the plurality of data lines, respectively. 